A Stampede of Accelerating Elephants

Over the Age of Exuberance, Westerners created and expanded a way of life based on the exploitation of cheap and readily-available fossil fuels by inventing and distributing increasingly efficient fossil fuel-burning technologies far and wide. In short, we used our ingenuity to enrich ourselves at the cost of the environment.

An economist would call this growth extensive; that is to say, based on the expansion of the quantity of inputs in order to increase the quantity of outputs. Now that the limits to growth are coming into sight, this type of growth is being subjected to diminishing returns. Worse still, it has no positive effect on per-capita magnitudes in the long-run because it reinvests efficiency gains back into the system.

This is the essence of the rebound effect – an empirically demonstrable phenomenon that describes changes in levels of consumption of a resource when the efficient use of that resource improves. What it shows is that efficiency gains in the short run spur increases in energy consumption in the long run, thus offsetting any environmental benefits.

It’s worth considering that at any point during the Age of Exuberance – at least in theory – those efficiency gains could have been retired for the benefit of the environment. We could have applied our considerable ingenuity toward making existing inputs go further, thereby reducing environmental impacts. This is what economists call intensive growth – the increasingly efficient use of a declining quantity of inputs in the production of a fixed number of outputs.

Under this model, as efficiency rises, those gains are retired out of the system. Retiring efficiency gains has a two-fold happy consequence: first, it helps the environment. Second, it results in greater amounts of leisure time within society (to the degree that the benefits are distributed equitably).

Those are the two choices: enrich ourselves or help the environment. Yet insular planning exhibits a distinct futility in gripping this fact; it mistakenly proposes policies that suggest that we can have our efficiency “cake” and eat it too.

I want to be clear that I do believe energy efficiency strategies have a part in any self-respecting sustainability strategy. However, I also want to show that history has demonstrated efficiency cannot all by itself lead to the hoped-for result of less energy consumption in the long, or even medium run. And like it or not, that’s the only way to relieve impacts on our finite planet.

To be sure, the pursuit of efficiency is a categorical imperative within insular planning. But not even it can hold a flame to perhaps the single overarching sacred cow of insular planning: the promotion of higher density.

Now, there’s nothing intrinsically wrong with density. It’s good – just not infinitely so. It’s an important factor in ensuring sustainability. But like efficiency, there are some nuances to employing density that insular planning fails to take into consideration. Nuances which, if ignored, can have deleterious consequences in realizing sustainability.

Density is such a loaded concept that I’m going to have to take a moment to make myself perfectly clear. The basis of my concern regarding density has NOTHING in common with the premises of Joel Kotkin or other boosters of suburbanization. In other words, by criticizing density’s role I am not advocating sprawl by default – quite the contrary. I don’t believe density and sprawl are two endpoints along some sort of mythical continuum. I’ll talk in some detail about this next week.

Before we get into a discussion of density, it might be useful to review some of the foundational concepts I’ve discussed in prior posts. Early on, I asked readers to step back and momentarily consider cities in physical terms rather than in purely social, economic, and political terms. While it’s true that cities are complex manifestations of human actions and interactions, those actions and interactions are grounded in physical reality. From this, we can conclude that cities are subject to physical and natural laws.

I introduced these concepts in the Laws of the Jungle series of posts a few weeks back. In short, I discussed in detail how cities operate as dynamic dissipative systems, are subject to the laws of thermodynamics, possess a metabolism, and interact with other systems ecologically.

We’re going to take these ideas a little further this week to show insular planning’s error in pursuing density at all costs. In doing so, I’ll be drawing on the work of a few scientists and physicists such as Geoffrey West, Luis Bettencourt, and James H. Brown. They’ve done a good bit of work on measuring the urban metabolism of cities and I think you’ll be interested in what they found.

The uninitiated should know that studies of urban metabolism facilitate the description and analysis of the flows of the materials and energy into, within, and out of cities. They also provide a holistic perspective to encompass all of the activities of a city in a single model.

The use of the word “metabolism” connotes a biological basis. The concept of imagining the city as a live being is nothing new – people have noted the metabolic character of cities for a long time running now. Plato talked about the city as a “corporeal body” thousands of years ago, for instance.

However, it wasn’t until 1965 that a sanitary engineer in Baltimore named Abel Wolman first formalized the concept in “The Metabolism of Cities”. He keenly noted that cities possess energy and material appetites in the form of a metabolism which governs its internal processes. For instance, cities consume resources like food, water, timber, and air, and produce finished goods, pollution and waste as outputs.  

In 1996, West et al. attempted to go even further in demonstrating how the urban metabolism concept was more than just an interesting biological metaphor by applying Kleiber’s Law to cities to see if they scaled in the same way as animals do.

Kleiber’s Law, named after Max Kleiber’s biological work in the early 1930’s, is the observation that an animal’s metabolic rate scales to the 3/4 power of the animal’s mass. In other words, doubling the mass of an animal requires only an 85% increase in energy requirements. This reflects efficiency in gaining size – an economy of scale.

The implication of this sub-linear relationship is that larger species need less energy per pound of flesh than smaller ones. For instance, while an elephant is 10,000 times the size of a guinea pig, it needs only 1,000 times as much energy.

West et al. found that the same economies of scale apply to the infrastructure of cities also. In city after city, the infrastructural indicators of urban metabolism, like the number of gas stations, total surface area of roads, or total length of phone, water, and sewer lines showed that when a city doubles in size, it’s infrastructural energy and resource demands rise by only 85%. This revelation suggests that the real purpose of cities over time has been to maximize economies of scale, just as big animals do.

West’s discovery of the applicability of Kleiber’s Law to cities would seem to confirm the steadfast belief within the insular planning community that our densest cities are the truest centers of sustainability because they promote efficient use of infrastructure.

The belief that density is inherently environmentally beneficial permeates planning literature. For instance, Peter Huber and Mark Mills’ influential 2000 essay “How Cities Green the Planet” triumphantly proclaims that the skyscraper is “America’s great green gift to the planet.”

Indeed, the standard policy within insular planning reads something like:
“By increasing density (along with efficiency and renewable energy) we can provide for a workable transition to a new arrangement of living comprising a world full of increasingly dense, technologically-intensive, affluent, and even ‘greener’ metropolises.”

If infrastructural efficiency was the only effect of increasing density, I’d be right up there with everybody else throwing roses and blowing kisses. However, Kleiber’s Law doesn’t tell the whole story when it comes to the metabolism of cities.

When West et al. expanded their research beyond just the infrastructural implications of increasing density, the picture changed.

They were surprised to find that Kleiber’s Law was inverted in cities regarding the average person’s rates of consumption. The research shows that if a person moved from one city into another one twice as big, all of a sudden they did 15% more of everything. In other words, the scaling laws observed for consumption run in the opposite direction to rates of change observed for infrastructure, thereby more than offsetting any environmental benefits.

In city after city, the consumption indicators of urban metabolism, like economic activity, income, water consumption rates, pollution, and garbage showed that when a city doubles in size, it requires an increase in resources and waste sinks of 115%.

The implication of this super-linear relationship is that larger cities need more energy and resources per capita than smaller ones because their average citizen owns, produces, consumes, and wastes 15% more than their less urbane counterparts. In effect, when cities densify, they become more consumptive, which offsets any infrastructural efficiencies provided by Kleiber’s Law.

The end result is a positive feedback loop: a bigger population means more economic activity for each person, which encourages more people to move to the city, which results in more economic activity, and so on. This explains why one half of all people on Earth now live in cities and why one million more are moving to cities weekly: they’re seeking out a way of life that allows them to leverage greater infrastructural efficiency into a higher material standard of living.

Every other creature in nature gets slower as it gets bigger. That’s why elephants plod along. But in cities, the opposite happens. As cities get bigger, everything starts accelerating. Metabolically speaking, big cities function like elephants that are proportionally faster and more consumptive than mice. Think about that for a minute. And then consider that insular planning is essentially encouraging the creation of a stampede of accelerating elephants in the form of multiple, growing metastatic cities.

Ecological principles tell us that absent of energy and resource constraints, dynamic dissipative systems are free to continue to expand until they hit hard, physical limits provided by the larger environment around them. These limits inevitably come, and when they do, the growth of the system tapers off in line with what the larger environment will allow.

Anyone who believes that cities are exempt from this constraint is fooling himself. The reason that cities have been able to invert Kleiber’s Law up to now is because, until recently, there have been few constraints on the energy and resources available to the many metastatic cities that now dot the planet. That’s a purely temporary strategy, as we’re currently bumping up against the edges of what we know is a closed system.

I’m certain that if West et al. were to study the metabolic rate of an algae bloom he would find it would resemble the exponential growth of metastatic cities over the Age of Exuberance. The only question is what happens when those hard limits are reached: will it resemble an S-curve – a slow, steady equalization with our larger environment? Or will it result in a crash? We cannot know the answers to these questions definitively, but we do know that our ancestors lived within limits and that we will increasingly do the same over the remainder of this century.

We need a new way of planning which presents a more-nuanced view of density. It would be madness to continue advocating a policy which so clearly conflicts with the hard limits of physical reality.

Though the ideas I’ve ushered forth this week should be considered only the crudest of starting points, I believe they have major implications for how we need to reimagine sustainability planning best practice. For starters, it suggests that the density ideal should be scrutinized closer for its alleged environmental benefit.

If you’ve gotten this far, you are probably well convinced that my critique of density does not imply advocacy of sprawl. I believe the density vs. sprawl dichotomy is a false one; I’ll spend a good bit of time next week unpacking this red herring.

For more about Geoffrey West and his theory, check out:
The Economist talk

NYT Magazine article
Radiolab episode

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